The present invention relates to apparatus for supplying electric power to lighting devices such as incandescent lamps and in particular to plug-in and interchangeable modules comprising a multifunctional housing containing the electrical components for controlling the light output levels from such lighting devices.
The apparatus according to the present invention is frequently referred to as a dimmer module. Dimming control systems utilizing self contained, interchangeable dimmer modules are already in use in architectural, theatrical and television applications. They control incandescent lamps and other types of lighting equipment including low voltage, fluorescent, cold cathode and other types of lighting loads. Such modules are typically provided in groups and are normally placed in racks of a number of different possible physical configurations. In one embodiment, dimmer modules are adopted to be inserted into aluminum shell and chassis systems which accept up to six plug-in dimmer modules and a plug-in control module. Output connectors are located on the rear panel of such racks and a cooling fan is likewise provided for blowing air through the chassis and carrying heat away from the module collection. Typically, a module provides two dimmer circuits of a lower power rating or one dimmer circuit of a higher power rating.
Such dimmer modules are characterized by the generation of significant amounts of heat, imposing a requirement that as much cooling as possible be provided. This cooling is typically obtained by the provision of external cooling means such as by fans, air conditioning and the like. Prior art dimmer modules have also been designed to utilize ambient air for cooling purposes but heretofore the layout of the components and the overall design of the module is such that there is a temperature gradient from one side of the dimmer module to the other thereby providing greater cooling at the one side of the module and reduced cooling because of the higher heat load at the other side.
Because such dimmer modules are used in large quantities, cost control of manufacture is also an everpresent objective. Prior art dimmer modules have been characterized by a design and physical layout and a mode of operation which entail the use of mounting hardware and conventional physical wiring of the various electrical components of the dimmer module with the attendant component and labor costs involved in providing such hardware and in making such wiring interconnections.
In a co-pending application there is described the electrical circuitry of a dimmer circuit and a method of operating the electrical circuit such as is used in the dimmer module according to the present invention in such a way as to handle greater electrical loads with the same size of components as in a conventional module or to meet the power requirements of conventional dimmer modules with a circuit design entailing substantially smaller components thereby effecting a reduction in the costs of the components and the overall assembly of the module and a comparable reduction in the heat generated by the apparatus. Thus, the features of that dimmer circuit and its method of operation make a significant contribution to overcoming the problems outlined above.
Other problems characteristic of the prior art dimmer modules resided in the manner in which the power devices were mechanically mounted and attached to a heat sink utilized to conduct heat away from the power device. Either mechanical mountings were used which typically lacked a solid thermal bond between the device and the heat sink, resulting in poor thermal transfer, or a thermal bond was attempted using heat sink grease. In this latter instance, the use of such grease was messy and awkward, particularly when the power device had to be removed and then replaced on the heat sink.
Prior art dimmers also normally utilized a separate printed circuit board on which certain components, such as the opto-isolators and gate resistors, were mounted. Typically, such a separate board was mounted above the main substrate which carried the switching devices. Such an arrangement required a number of wiring interconnections to the main substrate, all of which added significantly to the labor and expense involved in fabricating such a design.